On Friday, Pennsylvania’s two senators were touting a pair of nominees to fill federal district court vacancies in the state, showcasing the latest example of their across-the-aisle work on judicial nominations.

That bipartisan track record has been strained by the nomination of David Porter, a Pittsburgh attorney who is expected to take a step closer to a seat on the 3rd Circuit Court of Appeals despite the objections of Democratic Sen. Bob Casey.

Home-state senators are given the courtesy of signaling their approval of federal judicial nominees, which they do by returning a form known as a “blue slip.” Casey has withheld his blue slip.

Porter’s nomination is moving forward without Casey’s blue slip, as have the nominations of three other Trump administration picks that lacked support from at least one of their home-state senators.

Casey, liberal activists and some experts on the judiciary say that’s a troubling break from past practices. The blue-slip policy dates to 1917, and it has been “relatively rare” in recent decades for the full Senate to approve nominees who don’t have support from both of their home state senators, according to the Congressional Research Service.

The policy gives home-state senators who are more likely to be familiar with a nominee an avenue for weighing in, and encourages back-and-forth between senators and the White House.

Diminishing that practice “is horrible for the institution of the Senate,” said Carl Tobias, a University of Richmond professor of law who tracks federal judicial nominations.

Republicans involved in the Senate confirmation process, however, say the blue-slip tradition is a courtesy, not an absolute veto power.

Republican Sen. Chuck Grassley of Iowa, who chairs the Judiciary Committee, said during a hearing last week that he intends to move forward with a vote on Porter because the White House consulted with Casey beforehand.

“One senator generally does not have the right to block the other 99 of us from merely considering a circuit court nominee so long as the White House has consulted with that senator,” Grassley said.

Republican Sen. Pat Toomey also said it’s his understanding that there was “extensive consultation” with Casey by the White House.

“That consultation I know is taken seriously,” Toomey said.

Casey’s office disputes that he was adequately consulted on Porter’s nomination. His spokeswoman, Jacklin Rhoads, said that after Casey repeatedly expressed opposition to Porter, who the senator says advocates conservative legal policies that are hostile to workers and equal protection laws, the White House put forward one other name, whom Casey interviewed but found to be unqualified for the court.

“The White House did not propose additional names or ask Sen. Casey to provide the names of other individuals he would support,” Rhoads said. “Instead, they unilaterally nominated Mr. Porter over the senator’s objections.”

A White House spokeswoman did not respond to questions about the Porter nomination.

The blue-slip dispute isn’t the first step away from bipartisanship in the judicial confirmation process. Senate Democrats in 2013 ended the ability of senators to filibuster a trial or appellate court nominee they oppose; last year, Republicans removed the same tool for stopping Supreme Court nominations, after declining to consider President Barack Obama’s nomination of Merrick Garland.

Still, Toomey and Casey have long touted their efforts to work together on district court nominees, which typically are identified and recommended to the president by home-state senators. Staffers for Casey and Toomey say the two senators have worked together to get 14 district court judges confirmed since 2011.

When it comes to circuit court nominees, the White House tends to exert more influence over the selection — and its picks previously have created a split between Casey and Toomey.

In 2015, Obama nominated Rebecca Ross Haywood to the 3rd Circuit Court, sparking an objection from Toomey. He declined to return his blue slip, saying at the time that Haywood has “struggled” to answer questions about legal issues involving executive orders.

That objection had a different outcome, with Grassley deciding not to move forward with a hearing. A Judiciary Committee spokeswoman didn’t respond to questions about that nomination.

Toomey has supported Porter, describing him as someone with “the intellect, temperament, and legal experience to be an outstanding judge.”

Staffers from both Senate offices met Wednesday afternoon with activists organized by Why Courts Matter Pennsylvania, who came to express their opposition to Porter’s nomination. After those meetings, they moved to the lobby of Grassley’s Capitol Hill office, where they read aloud from a lengthy list of comments from Pennsylvanians who share their view.

If confirmed, Porter would serve on the appeals court that hears cases from Pennsylvania, New Jersey, Delaware and the Virgin Islands. He has worked as a business litigation attorney with the Pittsburgh firm of Buchanan Ingersoll & Rooney for two decades.